All spiders are capable of spinning silk, regardless of whether they use it to spin webs and trap prey or not. Egg sacs, drag lines (so they can find their way home), drop lines (to catch them if they fall) egg cases and transportation (young spiders disperse by “ballooning” as the wind catches their silk and carries them off) are some of the other functions silk plays in the life of a spider. Silk is extruded through nozzles called spinnerets located near the tip of the abdomen. Typically a spider has two or three pairs of spinnerets. Each one is the exterior tip of an interior silk gland and has a valve which can control the thickness and the speed with which the silk is extruded. The different glands produce different kinds of silk used for different purposes. The spinnerets work independently for some functions, and together for others. In the photograph, the black and yellow argiope is turning her grasshopper prey around and around as she produces a sheet of silk in which she wraps it. Most, if not all, of the spinnerets are in use.
Two common spiders that we often see carrying their egg sacs are the wolf spider and the nursery web spider. Wolf spiders attach their egg sacs to their spinnerets, whereas nursery web spiders carry them with their mouthparts. When nursery web spiders are about to hatch, the mother puts her egg sac into a silk tent she has spun, and they live there for a week or so. When a wolf spider’s spiderlings emerge from their egg sac, they climb up onto their mother’s abdomen and cling to it while their mother continues to hunt for food. After about a week, when partially grown, the spiderlings disperse, either by ballooning through the air on silk strands or simply by scurrying off along the ground.
All spiders spin silk — some use it to build webs, eggs sacs, draglines, wrap prey and/or disperse in the air. Inside their bodies are glands which produce different types of silk material for different purposes. Liquified silk proteins are pushed out spinnerets, or silk-spinning organs, located at the tip of a spider’s abdomen (most spiders have six). Once the silk solution comes in contact with the air, it solidifies. Each spinneret has a spigot, or nozzle, which controls the consistency of the silk by forming smaller or larger strands. By winding different silk varieties together in varying proportions, spiders can form a wide range of fiber material. Spider silk is extremely strong and flexible. Some varieties are five times as strong as an equal mass of steel and twice as strong as an equal mass of Kevlar.